Std 10 science chapter 1 gravitation explanation
1. Gravitation
std 10 science chapter 1 gravitation explanation
When an object gets attract toward another object because of it
has a lower mass than the object who has higher mass. The attraction between the two
objects are called gravitation.
Gravitation was first discovered by Sir
Isaac Newton. As he was sitting below the apple tree one apple fell from a tree
on the ground. Then he thought that why apple is falling down? Why it is not going
upward direction. This incident led him to find gravity.
Gravitational force definition: The force of attraction between two
objects which led one object to move toward another object is called
gravitational force.
Force and motion: an effect tending to change the motion
of the body or produce motion in the stationary object is called force. When an
object moves from one place to another is called motion.
Circular motion: Circular motion is the motion of a
particle along with the circumference of the circle is known as circular
motion.
Centripetal force: It is a force acting on a particle
performing circular motion which is acting along the radius of a circle and
directed toward the centre of the circle is called the centripetal force.
Kepler’s Laws: Planetary motion had been observed
since long time ago. Before the invention of the telescope in the 16^{th} century, all observation made with naked eyes. Lots of data were collected. Johannes
Kepler studied the data and gave three laws of planetary motion.
Kepler’s
first law: The orbits of a planet is an ellipse (oval) with the sun at one of the foci
(plural form of focus).
Kepler’s second law: While revolving around the sun, planet covers the equal area in equal an interval of time.
Kepler’s third law: The Square of its time of revolution around the sun is directly
proportional to the cube of the mean the distance thus if ‘r’ and ‘T’ is period of revolution then T^{2}αr^{3} i.e. T^{2}/r^{3}=constant=K
Newton’s universal law of gravitation: It says that this force is directly
proportional product of masses and inversely^{ }proportional
to Square of the distance between them^{.}
F=Gm_{1}m_{2}/d^{2}
Here G is constant and is called
the universal gravitational constant.
The value of G is always 6.673*10
Nm^{2 }kg^{2}.
Earth gravitational force: when we throw stone vertically upward it goes
up to a certain distance and fall down on ground back. It happens because of the
earth gravitational force. Earth attracts every object toward itself because of
its gravitational force. And because of this force, every object falls vertically
to the ground. When the stone goes up it is affected by earth gravity this led
the stone to reduce its velocity continuously. And when the velocity of stone
become zero it falls vertically
toward earth.
Always remember Mass of earth=6*10^{24}kg.
The radius of
the earth=6.4*10^{6}m.
Earth’s gravitational acceleration: The acceleration produced in the body under
the effect of Gravity or Gravitational force is called acceleration due to gravity. It is denoted by g.
The value of g=9.77m/s^{2}.
The value of g is constantly
changing according to the height of the object.
The value of g is also changed along the
surface of the earth: As the shape
of the earth is not exactly sphere at some point there is high and some point
there is low so this led to change in height of the object in surface to the centre
of the earth. The earth radius is higher at the equator and lower at the poles thus,
the value of g is highest at poles (9.832m/s^{2}) and lowest at the equator
(9.78m/s^{2}).
The
value of g change with height: As
we go higher in the sky from the centre of the earth the height increase from the
earth and as we know that height is inversely proportional gravitation hence
when an object goes high gravitation force decreases. But it acts on a certain
height forex. If we go 10 km up then the value of g is negligible. On the
another way if we consider the satellite which orbiting to the earth for them the
value of g is low because they are at a very high height from the centre of
earth.
The value of g in different places:
Place

Height(km)

G(m/s^{2})

The surface of the earth (average)

0

9.8

Mount Everest

8.8

9.8

The maximum height reached by manmade balloon

36.6

9.77

Height of typical weather satellite

400

8.7

Height of communication satellite

35700

0.225

Change
with depth: The value of
also change with depth as we go inside the earth. You must think that if we go
inside the earth the value of increase but it not. Because the part of the
earth contributes mass for gravitation is not present because we go inside the
earth which means the mass of the earth is less and hence the force of
gravitation is less.
What is meant by escape Velocity:
The minimum the velocity with which satellite should be Projected from the surface of the earth
so that its escapes from the earth is called escape velocity.
These all are the easiest definition of the
physics fundamentals.
Escape velocity formula:
Introduction to scientist:
Sir Issac newton:
Issac Newton 
Great scientists: Sir Issac Newton (16421727) was one of the greatest scientists of recent time. He was born in England. He gave his law of motion, equation of motion and theory of gravity in his book Principia. Before this book was written, Kepler had given three laws describing planetary motions. However, the reason why the planet moves in the way described by Kepler's laws was not known. Newton, with his theory of gravity, mathematically derived Kepler's laws. In addition to this, Newton did groundbreaking work in several areas including light, heat, sound and mathematics. He invented a new branch of mathematics. This is called calculus and has wideranging application in physics application and mathematics. This is called calculus and has wideranging applications in physics and mathematics. He was the first scientist to construct a reflecting Telescope.
Johannes Kepler:
Johannes Kepler 
Johannes Kepler (15711630) was a German astronomer
and mathematician. He started working as a helper to the famous Astronomer
Tycho Brahe in Prague in 1600. After the sudden death of Brahe in 1601. Kepler
was appointed as the Royal mathematician in his place. Kepler used the
observations of planetary positions made by Brahe to discover the laws of
planetary motion. He wrote several books. His work was later used by Newton in
postulating his law of gravitation.
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